Efforts will be continued to improve the culture of urothelial cells in vitro, to characterize the cultured cells and original tumor cells by karyological analysis, and to examine them for evidence of association of oncornavirus by means of reverse transcriptase assay and molecular hybridization. BIBLIOGRAPHIC REFERENCES: The biology of transitional malignancy. D. F. Paulson, R. A. Bonar, D. D. Mickey, J. R. Vergara, K. R. Stone and J. F. Glenn. Trans. Am. Assoc. G. U. Surgeons 66:121-125 (1974). In vitro culture of epithelial cells derived from urogenital tissues. K. R. Stone, D. F. Paulson, R. A. Bonar and C. F. Reich. Urological Research 2:149-153 (1975).